Extrusion device



April 1963 c. B. HENDERSON ETAL 3,087,306

EXTRUSION DEVICE FiledFeb. 5, 1959 2 Sheets-Sheet 1 L e 2122*5 Char/e5 B. Henaensm 5 106 M Burzon AGENT April 30, 1963 c. B. HENDERSON ErAL 3,087,306

EXTRUSION DEVICE Filed Feb. 5, 1959 2 Sheets-Sheet 2 Char/e5 5. Henderson 22 Joe M Burfozz W 02? m AGENT United States Patent 3,087,306 EXTRUSION DEVICE Charles B. Henderson, Alexandria, and Joe M. Burton,

Springfield, Va., assignors to Atlantic Research Iorporation, Alexandria, Va., a corporation of Virginia Filed Feb. 5, 1959, Ser. No. 791,489 16 Claims. (Cl. 60-39.47)

This invention relates to an extrusion member for extruding a plurality of masses or columns of cohesive, plastic, shape-retentive monopropellant from a storage tank into a combustion chamber at a uniform linear flow rate such that each of said masses or columns will reach an equilibrium burning condition at substantially the same linear flow rate of said monopropellant.

The term monopropellant refers to a composition which is substantially self-sufficient with regard to its oxidant requirements as distinguished from bipropellants where the fuel is maintained separately from the oxidizer source until admixture at the point of combustion.

There have recently been developed for use in gas generating apparatus, such as rocket motors, gas turbines and the like, a number of plastic monopropellants, which are particularly adapted for extrusion as cohesive, shape-retaining, continuously advancing masses or columns into a combustion chamber, where they are burned to generate high energy gases for developing thrust or power or for providing heat or gas pressure. The compositions have thixotropic properties and are sufficiently fluid above a certain finite stress to be fed at ambient temperatures through shaping apertures into a combustion chamber. The leading face of the shape-retaining column presents a burning surface of predeterminable area, which can be varied and controlled by varying the rate of extrusion.

These plastic monopropellants combine many of the advantages and eliminate many of the disadvantages of previously known liquid or solid propellants used to power similar devices.

Such plastic monopropellants are normally stored in' a fuel tank from which they are extruded through an apertured plate or other suitable extrusion member into a combustion chamber. The primary purpose of the extrusion member is to divide the propellant into a plurality of separate masses or columns, thereby to increase the total burning area of monopropellant available in a combustion chamber, of preferably minimum length.

The extruding column of monopropellant burns on all surfaces exposed in the combustion chamber. When burning equilibrium is reached at a given rate of extrusion, the surface of the propellant column Within the combustion chamber converges in the downstream direction forming a downstream edge or apex, depending on the shape of the extrusion orifice. Tlhe angle of convergence at equilibrium is determined only by the ratio of the linear rate of extrusion to the linear burning rate of the particular monopropellant, regardless of the size of the extrusion aperture. The higher the value of this ratio, the more acute is the downstream angle of convergence resulting in a longer column of burning propellant having a proportionately larger burning surface area. The mass rate of burning is proportional to the burning surface area and to the linear burning rate. Consequently, the linear rate of extrusion is at equilibrium the determinative factor for the mass rate of burning.

3,087,306 Patented Apr. 30, 1963 Most efficient operation is obtained in most applications by maximizing the total burning surface area of the plurality of extruding burning propellant masses within limits allowing for such increase as might be necessary during the performance cycle. Practical limits are, however, set by the physical characteristics of the plastic, semi-solid monopropellant. Although the monopropellant is cohesive and possessed of substantially high tensile strength, below certain ratios of maximum thickness of the protruding column to its length, namely below certain minimum angles of convergence, the extruding column may slump or fragment under vibrational and other stresses. Such limits are, of course, determined by the particular plastic monopropellant, and the rate of extrusion and, thereby, the angle of convergence, are programmed accordingly.

it has been found that where the extrusion member is provided with a plurality of passages or apertures, each having the same cross-sectional area, the same length of boundary surrounding this area, and the same length through the extrusion member, the flow rate of monopropellant urged from the fuel tank by a piston or other pressurizing arrangement will be higher through those passages which are located near the center of the extrusion member than it will be for the monopropellant extruded through the passages located at or near the periphery of the extrusion member. This is to say, where, for example, a round piston mounted in a generally cylindrical fuel tank is used to urge the plastic monopropellant longitudinally along the tank and out through an extrusion member mounted at the rearward end thereof, it has been found that the plastic material at the axial center of the cylindrical tank flows faster than the material at the periphery of the tank. This phenomenon is apparently due to the fact that the plastic material in contact with the walls of the tank is slowed down by frictional forces therebetween. The slower moving outer layer in turn slows down the next interior layer to a lesser extent. The process is repeated and, of course, the frictional forces exerted by the walls has the least efiect on the material at the axial center of the tank.

This differential in flow rate impairs the efiiciency of operation of the burner or gas generator being fed. The minimum =flow rate through every one of the apertures of the extrusion member must be at least equal to and preferably higher than the linear burning rate of the monopropellant in order to maintain the process of combustion within the combustion chamber and prevent burning back into the fuel chamber. TIhe minimum rate of extrusion must, therefore, be geared to that of the propellant venting into the combustion chamber through peripheral apertures in the extrusion member. Since the centrally positioned advancing columns of propellant will be extruding at a higher rate than the peripheral columns, at equilibrium burning, the latter will be considerably shorter in length, will have a larger downstream angle of convergence, and will provide a substantially smaller burning surface area, than the former. This reduces the total mass burning surface area, and, thereby the mass rate of gas generation, as compared with that obtainable if the peripheral columns were extruding at the same linear rate as the more centrally positioned columns. A larger total mass burning surface can, of course, be achieved by increasing the rate of extrusion,

thereby lengthening the burning surface area of each of the peripheral columns. It must be borne in mind, however, that this expedient also further lengthens the central columns and makes more acute the equilibrium angle of convergence. This, as aforedescribed, cannot be pushed beyond a certain limit, depending on the particular monopropellant composition. As a result, the peripheral columns must be maintained at linear rates of extrusion substantially below the maximum of that of the centrally located columns, and thus below the otherwise possible maximum rate.

It is therefore an object of this invention to provide apparatus for extruding a plurality of masses or columns .of plastic monopropellant from a fuel tank into a com- .of plastic monopropellant to be burned, said member being of novel geometrical configuration which affords increased efliciency and controllability of burning of said monopropellant.

Other objects, features, and advantages of the present invention will be more fully apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawings in which like reference characters refer to like parts throughout and wherein FIGURE 1 is a diagrammatic longitudinal sectional view of a rocket motor of the type in which an extrusion member in accordance with the present invention may be used.

FIGURE 2 is an isometric view of an extrusion member in accordance with a first embodiment of the invention. I

FIGURE 3 is an elevational View looking in the direction of the arrows IIII-II of FIGURE 2 and showing the exit or combustion chamber face of the extrusion member.

FIGURE 4 is a fragmentary perspective view showing the equilibrium'cone-shaped burning surfaces formed by a mass or column of extruding monopropellant.

FIGURE 5 is a side 'elevational view of a second embodimentof the invention.

FIGURE'G- is an end elevational view looking in the direction of the arrow VIVI in FIGURE 5 FIGURE 7 is as ideeiev-a-tional view of a third embodimentof the invention.

FIGURE 8 is an end elevational view looking in the direction of the arrows VI-IIVIII in FIGURE 7.

FIGURE 9 is a side'elevational View of a fourth embodiment of the invention.

FIGUREIO is an end elevational view looking in the direction of the arrows XX of FIGURE 9.

'Wehave found that a substantially uniform rate of flow through all of the'extrusion member apertures, both peripherally and centrally positioned, can be obtained by providing peripheral flow passages having either (1) a ratio of cross-sectional area to circumferential length bounding that area which is greater in value than the ratio of these dimensions for the more central passages, all

passages through the extrusion member having the same length, or (2) "a ratio of cross-sectional area to circum- "ferential'boundary length which can be the same or larger or smaller in value than the ratio of these dimensions for the more central passages, but the length of which peripheral passages through the extrusion member is not the same length as the more central passages but is greater or smaller, as required, to compensate for both the slower velocity of propellant near the boundary of the fuel chamber wall and the chan in f The 10 all of the passages can be obtained. The requisite dimensions can readily be determined by calculation and routine experimentation by any one skilled in the art. What is required is that the cross-sectional area of any passage (called A), the length of the boundary or perimeter of that area (called B), and the length of that passage through theextrusion member (called L), be related in such manner'that the ratio A/BL is somewhat greater for the peripheral passages than for the more centrally located passages. Of course, the greater the number of apertures fromthe center tothe periphery of the extrusion member,'the finer can be the gradation of dimensions and the more closely can perfect uniformity of flow rate be achieved.

Referring now to the drawings and in particular to FIGURE 1, there is shown a diagrammatic longitudinal view of a rocket engine of a type in'which the extrusion member of the present invention finds application.

The rocket engine may for example, comprise a generally cylindrical fuel tank 10 adapted to contain a plastic monopropellant 11 and having 'a piston 12 slidably a combustion chamber 14.

mounted therein to exert pressure on the monopropellant '11 and thereby force the monopropellant through an ex- :tr'usionmember 13 mounted in the rearward wall of the fuel tank to form an outlet-from the fuel tank to p The forward wall of the fuel tank .10may conveniently be formed by a separate tank or other storage container for a pressurized inert gas such as nitrogen. The pressurized inert gas'container K15'm'ay conveniently be connectedby a conduit 16, having a valve 17 therein to the'forward 'portionof the fuel'tank'ltl ahead of the piston -l2. By controlling the pressure of the gas applied to the piston 12, asby man- 'ually or automatically controlling the pressure drop "acr'ossthe valve17, therate of motion of piston 12 and 5 "hence the rate of extrusionof monopropellant 11 from thefueltank 10 throughthe extrusion member l3'ma'y in general be controlled. A'conventional igniter 19' is provided in the combustion chamber 14. The monoprofpellant 11 extruded through extrusion member 13 is burned in combustion chamber 14 to produce gases which escape through the nozzle 18 in'open communication with "combustion chamber "14-and, thereby, to generate thrust "for the rocket.

Extrusion member 13 is of the same length throughout from its forward'face exposed to the fuel chamber to its rearwardface exposed to the combustion chamber. The *peripheral'extrusion passages'13c each have a larger crosssectional area, and therefore a larger ratio A/B than that of eachof the next interiorly positioned passages 13b,

f-which' in turn are' soniewhat larger than the innermost central passage 13a.

Turning'now to'F'IGURES 2, '3, and '4, there is shown 'in'g'reater detail 'asimilar embodiment of the invention 'shown in FIGURE 1, wherein all of the passages are of ii the same length but the peripheral passages are provided from the fuel chamber, is beveled or charnfered, as shown at 21a, 22a, and 23a, to reduce frictional resistance to flow of the fuel as it enters the extrusion passage.

The passages or orifices are preferably substantially spaced from each other to provide for adequate strength of the extrusion member to withstand high extrusion pressures and to eliminate any tendency of the extruding plastic monopropellant columns to coalesce upon entry into the combustion chamber. The minimum distance between the apertures on the face of the extrusion member exposed to the combustion chamber is desirably about 50 mils and preferably about 100 mils.

FIGURE 4 shows schematically the equilibrium burning surfaces of the extruding monopropellant column-s. The burning surface of each of the columns slopes convergently downstream to form a cone. Since the linear flow rate through peripheral passages 21 is the same as that through the more central passages 22 and 23 because of the compensating effect of the increase in cross-sectional area, the respective apical cone angles 24, 25 and 26 of conical masses 27, 28 and 29 are equal. Inasmuch as the area of the base of conical mass 27 is larger than that of conical mass 28, the former must protrude into the combustion chamber for a greater distance than the latter to provide the equal cone angles formed at equilibrium burning by a given uniform linear rate of flow. A similar relationship exists between cones 28 and central cone 29. However, the greater height .of the peripheral cones is neither a detrimental nor a limiting factor. Since the cone angle and the ratio of width at the base to the height is the same as in the case of the more centrally positioned cones, the upper limit of extrusion rate beyond which the burning, extruding columns may slump or fragment is the same. Thus, the burner can be operated at maximum efficiency within linear extrusion rate limits set only by the particular linear burning rate and cohesive properties of the monopropellant.

It will be understood that the same principles of equilibrium burning as are diagrammatically illustrated in FIG- URE 4 using the orifice geometry shown in FIGURES 2 and 3, are equally applicable to plastic monopropellant masses or columns of other shapes which may be produced by extrusion passages of different geometry and different cross-sectional area, such as those to be described below.

[In FIGURES and 6, there is illustrated another embodiment of a fuel extrusion member 30 wherein the peripheral passages or orifices 31 and the central or inter-ior passage or orifice 32 are each of the same cross-sectional size and shape but wherein the central passage 32 is longer than the peripheral passages 31. This desired variation in length may, for example, be achieved by providing a frusto-conical projection 33 on the fuel tank end of the extruder member 30. The central passage 32 then terminates in the flat portion of this projection. The

1 peripheral passages 31 terminate in the slanting sides of projection 33. The frusto-concial projection may be shaped and dimensioned to provide the desired difference in length between the central and peripheral passages necessary to achieve a uniform linear extrusion rate for any particular monopropellant to be extruded.

The use of hexagonal orifices disposed in the geometrical relationship shown in FIGURE 6, wherein one hexagonal orifice is positioned so that one of its sides is in spaced parallel relationship to one of the sides of the central hexagonal orifice and this positioning is repeated for each of the sides of the central orifice to form a group of seven orifices, has certain special advantages.

The arrangement is such that for an extrusion member having overall circular cross-sectional shape, the disposition and geometry of the hexagonal orifices give, for orifices of uniform cross-sectional area, the highest possible efficiency by providing a maximum ratio of extrusion orifice area to total crosssectional area of the extrusion member,

, while maintaining adequate minimum spacing between the orifices. The same type of pattern can, of course, be

6 extended to a larger extrusion member to provide tor additional, more peripheral orifices.

At equilibrium burning, the monopropell-ant columns extruding through the hexagonal orifices will form substantially cone-shaped masses. However, unlike the situation as shown in FIGURE 4, the equal-angled cones, both central and peripheral, will be of substantially the same height, since the cross-sectional area of the base in each case is the same.

It will be understood that the principle of varying the length of the extrusion passages can also be applied .to circular orifiecs or to orifices of any other cross-sectional geometry,

In FIGURES 7 and 8, there is illustrated a fuel extrusion member 40, wherein the central extrusion passage 41 is of hexagonal shape and the peripheral passages 42 again each have one side which mates in spaced parallel relationship with one side of the central orifice, but in this construction the peripheral orifices are essentially segments of a circle rather than hexagonal in order to give them a larger ratio of cross-sectional area to circumferential boundary length than that of the central orifice 41. It will lb noted from FIGURE 7 that again in this embodiment the length of the central and peripheral passages is the same and uniformity of fiow rate is achieved by varying the ratio of the cross-sectional area of the passages to .the circumferential boundary length of this area. The hexagonal central orifice and segmental peripheral orifices, however, afford a somewhat better ratio of total extrusion passage cross-sectional area to total cross-sectional area than does the configuration of FIGURE 3.

If one desires to have a central aperture which is circular in cross-section and still utilize the advantages gained from the type of arrangement shown in FIGURE 8, a geometry of the type shown in FIGURES 9 and 10 can be used. In this embodiment of the fuel extrusion member 50, a central extrusion passage 51 is of circular crosssection and is surrounded by a first set of four extrusion orifices 52 each of which is substantially a quarter segment of a circle. The intermediate orifices 5-2 are in turn surrounded in concentric relationship with the peripheral orifices 53, each of which is again essentially a quarter segment of a circle. It is evident that the lengths of each of the passages 51, 52, and 53 are the same, but the ratio A/B of cross-sectional area (A) of each of the passages 52 to the circumferential boundary (B) of that area must be somewhat greater than the corresponding ratio characteristic of passage 51, and the ratio A/B of each pasmade of a material of low thermal conductivity, the

maximum thermal conductivity preferably being about 3 B.t.u./hour/sq. ft./ F./ft. The low thermal conductivity of the extrusion member prevents conduction of heat firorn the combustion chamber along the walls of the" orifice passages through which the propellant extrudes, so that the propellant in contact with the walls within the extrusion orifice is not heated to ignitiontemperature.

- Examples of suitable materials of low thermal conductivity include many refractory and ceramic compositions, such as aluminum and other silicates, fireclays, 'Alund-um, magnesite, sillimanite, silica, quartz and zircom'a.

A low thermal conductivity material which gasifies under the conditions of elevated temperature developed in the combustion chamber is particularly desirable as a means for preventing burn-back ofthe extruding propellant. Gasification of the extru-stion member material,

under pressure at ambient temperatures. -ferent plastic monopropellant compositions tailored to "either-by decomposition or by change of state from a solid to a gas, or from a solid to -a liquid and then to a gas, requires a substantial amount of heat energy. The req- 'uisite heat is absorbed from the 'hot combustion gases adjacent to the face of the extrusion member exposed in the combustion chamber, and the hot gases are thus cooled. The gases evolved by volatilization of the extrusion member material are relatively cool and, upon admixture with the already cooled gases adjacent to an extrusion orifice, reduce the temperature of the gases in contact withthat portion of the extruding mass of propellant adjacent to the rim of the orifice at the point of entry of the propellant into the combustion chamber, thereby tending to quench peripheral burning of the advancing propellant mass at the orifice and preventing any burn-back along the'walls of the orifice passage that might otherwise take place. Most effective quenching is obtained with extrusion member materials which volatilize at tem peratures below or not substantially higher than the ignition temperature of the monopropellant.

Substantially any organic compound volatilizes or decomposes to-form gases at the high temperaturre developed by burning of the monopropellant in the combustion chamber, so that any such compound having the desired low thermal conductivity can 'be employed.

Many organic polymers are particularly suitable as structural materials including, for example, polyamides, such as nylon; acrylic and methaorylic resins, such as polymethyl methacrylate; cellulose esters, such as cellulose acetate; cellulose ethers, such as ethyl cellulose; polyesters, such as the alkyd resins; vinyl polymers, such as polystyrene and polyvinyl chloride; fluorohydrocarbons, such as polytetrafluoroethylene (Teflon); polyurethanes; phenolaldehydes; phenol-ureas; silicones; and the like.

Finely-divided solid organic compounds and inorganic compounds having good gasifying properties can be dispersed in the basic structural material, which can be a different gasifying material, such as an organic polymer or a mixture of such a gasifying material with a refractory non-gasfiying material. Examples of organic gasifying compounds suitable for such dispersion include such compounds as oxarnide, melamine, anthraquinone, p-benzoyl aminobenzoic acid, and a multitude of others. Examples of just a few of the many available gasifying inorganic compounds are calcium, sodium, and ammonium rphosphate, carbonate and bicarbonate salts, ammonium chloride, antimony oxychlon'de, etc.

The extrusion plate material can also be a mixture of a nongasifying refractory material, in felted or woven form, or in flake or fiber form, such as asbestos, fiberglass,

mica and the like, anda gasifying material, such .as a solid organic polymer. Upon gasification of the organic polymer, the non-gasifyi-ng component remains as a rigid structure of low thermal'conductivity, which preserves the original contours of the extrusion plate.

The monopropellant employed in the devices of this invention is preferably a plastic mass which'is sufficiently cohesive to retain a shaped form and which is extrudable Many dif benzyl alcohol, triethylene glycol and the like; ethers such as methyl a-napht-hyl ether and the like; and many others. The solid oxidizer can be any suitable, active oxidizing agent which yields an oxidizing element such as oxygen, chlorine or fluorine readily for combustion of the fuel and which is insoluble in the liquid fuel'vehicle. Such oxidizers include inorganic oxidizing salts such as ammonium, sodium and potassium perchlorate or nitrate and metal peroxides such as barium peroxide.

The amount of solid oxidizer incorporated varies, of course, with the particular kind and concentration of fuel components in the formulation, the particular oxidizer, and the specific requirements for a given use, in terms, for example, of required heat release and rate of gas generation, and can readily be computed by those skilled in the art. Since the liquid vehicle can, in many instances, beloaded with as high as to of finely-divided solids, stoichiometric oxidizer levels with respect to the fuel components can generally be achieved when desired, as for example, in rocket applications where maximum heat release and specific impulse are of prime importance. In some applications, stoichiometric oxidation levels may not be necessary or even desirable, as, for example, in gas turbines where relatively low combustion chamber temperatures are preferred, and the amount of oxidizer can be correspondingly reduced. Sufiicient oxidizer must, of course, be incorporated to maintain active, gas-generating combustion.

Finely-divided solid metal powders such as aluminum or magnesium, may be incorporated in the monopropellant composition as an additional fuel component along with the liquid fuel. Such metal powders possess the advantages both of increasing the fuel density and improving the specific impulse of the monopropellant because of their high heats of combustion.

The physical properties of the plastic monopropellant in terms of shape-retentive cohesiveness, tensile strength and thixotropy, can be improved by addition of a gelling agent, such as a polymer, e.g. polyvinyl chloride, polyvinyl acetate, cellulose acetate, ethyl cellulose, or metal salts of higher fatty acids, such as the sodium or magnesium stearates or palmitates. The desired physical properties can also be obtained without a gelling agent by using a liquid vehicle of substantial intrinsic viscosity, such as liquid organic polymers, e.g. liquid polyisobutylene, liquid siloxanes, liquid polyesters, and the like.

Many different plastic monopropellant compositions may also be used. It is, therefore, to be understood that this invention is not limited to use with any particular plastic monopropellant composition, but rather is directed to an apparatus particularly adapted for use in extruding any plastic monopropellant.

.The following is a specific exemplary embodiment of the invention:

The test apparatus was a cylindrical rocket motor of 2 inch internal diameter, comprising a combustion chamber, provided with an exhaust nozzle 0.145 in. in diameter, separated from a fuel chamber containinga plastic monopropellant by a cylindrical nylon extrusion plate '2 inches thick and provided with 18 circular orifices arranged substantially as shown in FIGURE 3, the minimum spacing between orifices being 0.1 inch, the 11 peripheral orifices being 0.3125 inch in diameter, and the 7 more centrally positioned orifices being 0.250 inch in diameter.

The heterogeneous, cohesive, shape-retaining, plastic monopropellant was a mixture consisting in parts by weight, of 75 parts of finely-divided ammonium perchlorate, 7.5 parts viscous liquid polyisobutylene, average mol. wt. 8700-40000, 11.25 parts viscous liquid polyisobutylene, average mol. Wt. 840, 6.25 parts dibutyl phthalate, and 0.5 part copper chromite.

The propellant was extruded into the combustion chamber at a mass flow rate of 0.0217 lb./sec. and a substantially uniform linear flow through the peripheral and centrally positioned orifices, other than the axial orifice, of 0.343 in./sec., the flow rate through the most central orifice being somewhat higher. The propellant columns extruding into the combustion chamber were ignited and burning of the extruding propellant continued for 37 seconds. The measured median combustion chamber pressure was 156 p.s.i.a. The linear burning rate of the monopropellant as measured in a strand burner at the same pressure was 0.168 in./ sec.

While a particular exemplary embodiment of the invention has been described in detail above, it will be understood that modifications and variations therein may be effected without departing from the true spirit and scope of the novel concepts of the present invention as defined by the following claims.

We claim:

1. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages.

2. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, each of said passages being of the same length, the more peripheral passages having a larger ratio of cross-sectional area to perimeter of said cross-sectional area than the corresponding ratio of the more central passages.

'3. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, each of said passages having the same uniform cross-sectional shape and area, the more peripheral passages being shorter in length than the more central passages.

4. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, said passages being sufiiciently spaced at the point of entry of said extruding, shaped propellant masses into the combustion chamber to prevent coalescence of said masses, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is central passages, said apertured member greater than it is for each of the more central passages.

5. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member having walls therein defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, said walls separating said plurality of pas-sages being of a uniform predetermined minimum thickness in order to provide a maximum ratio of pass-age cross-sectional area to total cross-sectional area of said apertured member, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages.

6. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/ BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, said apertured member being made of a material having a maximum thermal conductivity of about 3 B.t.u./hour/ sq. ft./ F./ ft.

7. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, each of said pass-ages being of the same length, the more peripheral passages having a larger ratio of cross-sectional area to perimeter of said cross-sectional area than the corresponding ratio of the more central passages, said apertured member being made of a material having a maximum thermal conductivity of about 3 B.t.u./hour/ sq. ft./ F./ft.

8. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, each of said passages having the same uniform cross-sectional shape and area, the more peripheral passages being shorter in length than the more being made of a material having a maximum thermal conductivity of about 3 B.t.u./hour/ sq. ft./ F./ft.

9. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear fiow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses,-certain of said passages being peripherallydis'posed relative to other, more centrally dlS- -psedpassages, the relationship of size of each of the more peripheralpassages in the apertured member to each of the more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, -B- isthe perimeter-of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, said apertured member being made of a material having a maximum thermalconductivity of about 3 B.t.u./hour/sq. ft./ F./ ft., andcapable of producing gases when heated by the hot combustion gases in the combustion chamber.

10. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into acombustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, each of said passages being of the 'same length, the more peripheral passages having a larger ratio of cross-sectional area to perimeter of said crosssectional area than the corresponding ratio of the more central passages, said apertured member being made of a material having a maximum thermal conductivity of about 3 B.t.u./hour/sq. ft./ F./ft., and capable of producing gases when heated by the hot combustion gases in the combustion chamber.

11. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from afuel tank into a combustion chamber at a substantially uniform linear flowrate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a pluralityof passages therethrough to accommodate flow of said monopropellant and toshape 'said'extruding masses, each of said passages'having the same uniform cross-sectional shape and area, the more peripheral'passages being shorter inlength than the more central passages, said apertured member being made of -'a material having a maximum thermal conductivity of about 3 'B.t.u./hour/sq. ft./ F./ft., and capable of producing gases when heated by the hot combustion gases in I the combustion chamber.

12.In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear,

fiow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, asdefined' by theexpression A/BL, where A is the cross-sectional area of the passage, B' is the perimeter of said area A, and L is the length of the passage, "being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, said apertured member being made of a refractory material having a maximum thermal conductivity of about 3 B.t.u./hour/ sq. ft./ F./-ft.

"13. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a'fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodatefiow of said monopropellant and to shape saidextruding masses, certain of said passages being peposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the'more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A,and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than itis for each of the more central passages, said apertured member being made of a material comprising an organic polymer having a maximum thermal conductivity of about 3 B.t.u./hour/sq. ft./ F./ft., and capable of producing gases when heated by the hot combustion gases in the combustion chamber.

14. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/BL, where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, said apertured member being made of a material comprising an organic polymer having a maximum thermal conductivity of about 3 B.t.u./hour/sq. ft./ F./ft., and capable of producing gases when heated by the hot combustion gases in the combustion chamber, said polymer having dispersed therein a different finely-divided material capable of producing gases when heated by the hot combustion gases.

15. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into acombustion chamber at a substantially uniform linear flow rate, an apertured member positioned betweensaid fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the more peripheral passages in the apertured member to each of the more central passages, as defined by the expression A/BL, Where A is the cross-sectional area of the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, said apertured member being made of a material comprising an inorganic refractory component and a solid organic polymer, said material having a maximum thermal conductivity of about 3 B.t.u./hour/sq. ft./ F./ft., said organic polymer being capable of producing gases when heated by the hot combustion gases in the combustion chamber.

16. In apparatus for extruding a plurality of shaped masses of plastic monopropellant from a fuel tank into a combustion chamber at a substantially uniform linear flow rate, an apertured member positioned between said fuel tank and said combustion chamber, said apertured member defining a plurality of passages therethrough to accommodate flow of said monopropellant and to shape said extruding masses, certain of said passages being peripherally disposed relative to other, more centrally disposed passages, the relationship of size of each of the .more peripheral passages in the apertured member 13 14 to each of the more central passages, as defined by the References Cited in the file of this patent expression A/BL, where A is the cross-sectional area of UNITED STATES PATENTS the passage, B is the perimeter of said area A, and L is the length of the passage, being such that the value ggggg 3333 g2 of said expression for each of the more peripheral passages is greater than it is for each of the more central passages, FOREIGN PATENTS said apertured member being made of a polyarnide. 582,621 Great Britain Nov. 22, 1946 

1. IN APPARATUS FOR EXTRUDING A PLURALITY OF SHAPED MASSES OF PLASTIC MONOPROPELLANT FROM A FUEL TANK INTO A COMBUSTION CHAMBER AT A SUBSTANTIALLY UNIFORM LINEAR FLOW RATE, AN APERTURED MEMBER POSITIONED BETWEEN SAID FUEL TANK AND SAID COMBUSTION CHAMBER, SAID APERTURED MEMBER DEFINING A PLURALITY OF PASSAGES THERETHROUGH TO ACCOMMODATE FLOW OF SAID MONOPROPELLANT AND TO SHAPE SAID EXTRUDING MASSES, CERTAIN OF SAID PASSAGES BEING PERIPHERALLY DISPOSED RELATIVE TO OTHER MORE CENTRALLY DISPOSED PASSAGES, THE RELATIONSHIP OF SIZE OF EACH OF THE MORE PERIPHERAL PASSAGES IN THE APERTURED MEMBER TO EACH OF THE MORE CENTRAL PASSAGES, AS DEFINED BY THE EXPRESSION A/BL, WHERE A IS THE CROSS-SECTIONAL AREA OF THE PASSAGE, B IS THE PERIMETER OF SAID AREA A, AND L IS THE LENGTH OF THE PASSAGE, BEING SUCH THAT THE VALUE OF SAID EXPRESSION FOR EACH OF THE MORE PERIPHERAL PASSAGES IS GREATER THAN IT IS FOR EACH OF THE MORE CENTRAL PASSAGES. 